The present invention relates to a receiver having analog and digital video modes and a receiving method therefor, and more particularly, to a receiver sharing a memory for digital television signal processing in an analog video mode, and to a receiving method therefor.
The digital video mode is to receive television signals, digitally processed by the MPEG (Moving Picture Experts Group) standards from a transmitter such as a broadcasting station, and the analog video mode is to receive signals analog-processed by a conventional broadcasting method such as NTSC, PAL or SECAM. While a set-top-box for decoding a bitstream coded by MPEG-2, or a digital television including a set-top-box are being developed, conventional analog video service is still overwhelmingly predominant. In answer to this situation, a television receiver having both analog and digital video modes is needed. Such an analog and digital video mode television receiver requires 8-32 Mb of memory for digital television signal decoding. This memory, however, is idle (i.e., unused) when the analog video mode is selected.
In an analog receiver having an analog video mode, as shown in FIG. 1, a tuner 11 selects a desired television channel signal among received analog television channel signals, to output an intermediate frequency signal. A channel demodulator 12 amplifies and demodulates the intermediate frequency signal of the channel selected by tuner 11. (While the amplified and demodulated signal is separated into audio and video signals, only the video portion will be described for the sake of simplifying the drawings and description.) A luminance/chrominance (Y/C) separator 13 separates the video signal output from channel demodulator 12 into luminance (Y) and chrominance (C) signals, using a correlation between a current line and its adjacent ones and/or between the previous frame and a current frame stored in a frame memory 14. The separated signals are stored in frame memory 14 and at the same time are input to the display connector 15.
The display connector 15 converts the Y and C signals received from Y/C separator 13 into analog R, G and B signals and then outputs the converted signals to a display 16 which is, for example, a picture tube.
Tuner 11, channel demodulator 12, Y/C separator 13 correspond to an analog television signal processor 100. In addition, an analog-to-digital converter can be included for converting the output of channel demodulator 12 into digital form in order to store it in frame memory 14 as digital data, and a digital-to-analog converter for converting the output of display connector 15 into analog form in order to display it as an analog signal on display 16.
When a comb filter is used for the Y/C separation in a conventional analog television, a cross color or cross luminance phenomenon occurs due to insufficient Y/C separation. Accordingly, as shown in the circuit of FIG. 1, a frame memory is used for three-dimensional Y/C separation often noted as frame comb filtering, to enhance picture quality.
Frame memory 14 may be also used for post-processing, for further enhancement of the picture quality after the Y/C separation. That is, edge components determined by the correlation between a current frame and a previous frame using frame memory 14, are emphasized. Most such methods for enhancing picture quality require a costly high-capacity memory. Therefore, a method incorporating a limited memory is generally used, even though it is not as effective.
FIG. 2 is a schematic block diagram of a conventional digital television for receiving television signals coded by MPEG-2. In FIG. 2, a tuner 21 selects a desired channel signal from television signals received from an antenna. The television signals received from the antenna are input in an MPEG-2 packet structure.
According to an MPEG-2 format, the transmitting data has a system layer structure consisting of packets of a 188-byte unit. The packet structure includes a header having sync and side information and another region having audio data, video data and user data. The video data is compressed by an inter-picture encoding or intra-picture encoding technique. During the inter-picture encoding of predicted- and bi-directionally predicted picture data within each group of pictures (GOP) unit (fifteen pictures maximum) following an intra-picture, only the differences between the picture being encoded and another picture are encoded. Each GOP includes intra-picture data which can be independently coded without reference to any other picture data, predicted-picture data which can be coded from the preceding intra-picture data and the preceding predicted-pictures data by using motion compensation between adjacent pictures, and bi-directionally predicted picture data which can be coded from a preceding intra- or predicted-picture data and the following intra- or predicted-picture data, using motion compensation, between adjacent pictures.
A channel demodulator 22 including a quadrature phase shift-keying demodulator, a Reed-Solomon decoder and a Viterbi decoder, converts a desired digital television channel signal which is output from tuner 21, into an MPEG-2 bitstream.
A system decoder 23 separates the MPEG-2 bitstream into audio and video data streams. (As in the case of FIG. 1, the audio portion will not be described, though it is assumed that an audio decoder and audio signal processor are provided for decoding and signal-processing the audio stream, and only the video signal process is shown and will be described).
A video decoder 24 includes a variable-length decoder for variable-length-decoding the video data stream output from system decoder 23, an inverse quantizer for inverse quantizing the variable-length-decoded data, an inverse discrete cosine transform (IDCT) operator for performing IDCT operation, and motion compensator for computing motion-predicted data. Video decoder 24 reconstructs the compressed data in order to display the original data on a display 27. The reconstructed video is converted into an analog RGB signal by display connector 26 before being displayed on display 27.
A memory 25 is used for video-decoding, i.e., source-decoding, the digital video data performed in video decoder 24.
Memory 25 includes a video buffering verifier (VBV) buffer (also call a channel buffer) for converting the constant bit rate of the video data stream output from system decoder 23 into a variable bit rate before variable-length-decoding, and frame buffers for reconstructing the predicted and bi-directionally predicted pictures after compensating for motion by adding block data obtained by reading out a predetermined size of DCT blocks corresponding to a motion vector from previous frame data and inverse-DCT data. Accordingly, memory 25 requires a capacity of 8 Mb to 32 Mb for the frames and VBV buffers in order to decode the video data stream.
Tuner 21, channel demodulator 22, system decoder 23 and video decoder 24 correspond to a digital television signal processor 200. Further, the combination of digital television signal processor 200 and memory 25 is generally called a set top box (STB).
Since it is expected that the analog TV service such as NTSC, PAL will continue to exist, a consumer television system must have capability to display both analog and digital video services. Two methods therefor will be described as follows.
Referring to FIG. 3, all processes for digital video service are performed in an STB 210 and then the reconstructed video signal is applied to a video input terminal of a conventional analog television 110. Accordingly, digital video service can be received in the analog television 110 also.
Referring to FIG. 4, a television having a conventional analog video mode is provided with the digital television signal processor 200 and the memory 25, to thereby receive both analog video service and digital video service.
Accordingly, as shown in FIGS. 3 and 4, the memory is used for analog television signal processing, i.e., Y/C separation and post-processing, and an 8-32 Mb memory is used for decoding of digital video. When a television receives only analog video service, the memory of an 8-32 Mb for digital video-decoding is not used. It is thus inefficient because an existing resource within the television system cannot be used.